Part 1 and Part 2 of this article first appeared on Speaking of Diabetes

The onset of type 1 diabetes is mysterious, but one thing is for sure: some environmental factor triggers the immune system attack on beta cells. This environmental trigger is a longstanding mystery that research at Joslin Diabetes Center is beginning to unravel. Aleksandar D. Kostic, Ph.D., is studying how the communities of bacteria that line our digestive systems, also known as the microbiome, could start a chain reaction that leads to autoimmunity and type 1 diabetes.

This is the hypothesis that Dr. Kostic is working on in his newly established lab at Joslin Diabetes Center.

“The gut is the largest immune organ in the body,” says Dr. Kostic. “It plays an important role in distinguishing self from non-self, distinguishing all of our symbiotic bacteria from pathogens and food antigens and [many other] exposures.” These things develop the immune system by helping it to learn what to fight and what to leave alone… (from Part 1)

…There are key pieces of evidence to support Dr. Kostic’s idea that the microbiome is linked to the onset of type 1 diabetes. The first involves non-obese diabetic (NOD) mice. These mice are genetically similar to people who are prone to type 1 diabetes. Not every NOD mouse will get diabetes, just like not every person with high-risk genetics will develop the disease. But curiously, the rate of diabetes onset for these mice varies from lab to lab: ninety percent of the mice in one lab will contract diabetes whereas only sixty percent will in a lab on the other side of the country.

At first, researchers blamed differing genetics between mouse populations. “But then when people transfer the mice from one center to the other, the mice take on the same rate of incidence as the facility that they go to,” says Dr. Kostic. “Then it seemed obvious that it’s some kind of environmental effect.”

When groups of these mice from various centers around the country were studied in a germ-free isolator, they developed diabetes at an astounding rate. “They get it really early on, they get very much more…severe inflammation in the pancreas, and it happens much earlier,” he says. This seems to support the hygiene hypothesis, or the idea that children (or in this case, mice) who are raised in too-sterile environments have a higher likelihood of immune system problems down the line.

Researchers then transplanted microbiomes from mice with no genetic risk of developing diabetes into these germ-free NOD mice. (from Part 2)